xamarin/Xamarin.Auth — pull request #79 by jbogard (2014-11-11 21:25:03+00:00)
Title: Adding method to request a refresh token

Closes #47. You still typically need to subclass and override GetInitialUrlAsync:
```
public override Task GetInitialUrlAsync()
{
string uriString = string.Format(
"{0}?client_id={1}&redirect_uri={2}&response_type={3}&scope={4}&state={5}&access_type=offline&approval_prompt=force",
this.AuthorizeUrl.AbsoluteUri,
Uri.EscapeDataString(this.ClientId),
Uri.EscapeDataString(this.RedirectUrl.AbsoluteUri),
this.AccessTokenUrl == null ? "token" : "code",
Uri.EscapeDataString(this.Scope),
Uri.EscapeDataString(this.RequestState));
var url = new Uri(uriString);

return Task.FromResult(url);
}
```
But I found that method varied per OAuth provider a bit, and I still want other changes so I didn't bother messing with the URI.